The invention is based on a method for diagnosing a metering valve which defines a metering rate of a reagent which is to be metered into an exhaust gas region of an internal combustion engine, and of an apparatus for carrying out the method.
The subject matter of the present invention also comprises a computer program and a computer program product.
DE 101 39 142 A1 describes an exhaust gas treatment device of an internal combustion engine in which, in order to reduce the NOx emissions, an SCR (Selective Catalytic Reduction) catalytic converter is used which reduces the nitrogen oxides contained in the exhaust gas to nitrogen with the reducing agent ammonia. The ammonia is acquired in the exhaust gas region of the internal combustion engine from a urea hydrous solution which is sprayed into the exhaust gas region upstream of the SCR catalytic converter. The urea hydrous solution which is stored in a reservoir tank is placed at a predefined reagent pressure with a pump. In order to meter the urea hydrous solution as a function of the demand, a metering valve is provided which is set to a predefined throughflow rate.
Laid-open patent application DE 10 2005 001 119 A1 provides a diagnosis of valves that are used in an arrangement which meters fuel as a reagent in the exhaust gas region of an internal combustion engine. The oxidizable hydrocarbons are provided for heating an exhaust gas treatment device. The diagnosis provides for the reagent pressure which occurs between a reagent safety valve and a reagent metering valve to be monitored. The reagent pressure is measured during different switched states of the reagent safety valve and of the reagent metering valve. A diagnosis step provides for the reagent to be placed at a predefined reagent setpoint pressure. Afterwards, checking is carried out with the closed valves to determine that a drop in pressure of the reagent does not exceed a predefined pressure gradient.
Laid-open patent application DE 10 2004 061 247 A1 provides for comprehensive diagnosis of valves which are used in an arrangement which also meters fuel as a reagent into the exhaust gas region of an internal combustion engine. The reagent pressure which occurs in the reagent center path between a reagent safety valve and a reagent metering valve is measured in different switched states of the valves. A diagnosis step also provides here that after the closing of the valves it is checked whether a drop in pressure of the reagent occurs which is evaluated with respect to whether the drop in pressure does not exceed a predefined pressure gradient.
Laid-open patent application DE 103 60 891 A1 describes a method for diagnosing a metering valve, which defines a throughflow rate of a reagent which is to be introduced into an exhaust gas region of an internal combustion engine. The reagent which is placed at a predefined pressure by a pump is fed to the metering valve, wherein the pressure is detected by a pressure sensor. The diagnosis provides for a measure of throughput quantity to be evaluated during a diagnosis time. After the occurrence of a diagnosis starting signal, the metering valve is closed and the reagent is placed at a predefined diagnosis starting pressure by means of a pump. The metering valve is subsequently set to a predefined throughflow rate and the pressure difference occurring during the diagnosis time is evaluated. A first configuration provides for the diagnosis time to be permanently predefined and for faults to be detected if the pressure difference during the fixed diagnosis time exceeds a predefined pressure difference limiting value. It is alternatively possible to provide that the pressure difference is permanently predefined and that faults are detected if the diagnosis time exceeds a predefined diagnostic time limiting value. The reagent pressure which a pressure sensor detects is evaluated.
Laid-open patent application DE 10 2008 005 989 A1 describes an SCR system in which the reagent is placed at a reagent setpoint pressure by a pump. The pump contains an overflow valve which, when the set reagent setpoint pressure is reached, opens in the metering mode, with the result that an overflow to the suction inlet of the pump can take place. The overflow valve is implemented as a diaphragm which is clamped against a spring. A metering valve which defines the metering rate of the reagent is metered by evaluating a drop in pressure of the reagent. During the diagnosis, the pump is firstly switched off. Metering is subsequently carried on during a diagnosis metering mode, wherein the metered reagent quantity is determined in the diagnosis metering mode and the evaluation of the pressure drop is not ended until a metering quantity threshold value is reached.
Laid-open patent application DE 10 2009 000 097 A1 describes an SCR system which is less sensitive to contamination. In order to clean a reagent, a first filter is provided upstream of a reagent metering module and a second filter is provided upstream after a valve. A further filter and a throttle (not settable) for limiting the return flow rate are present in a return line which leads from the reagent pump back to the reservoir tank.
The invention is based on the object of specifying a method and a device for carrying out the method which permit diagnosis of a metering valve which defines a metering rate of a reagent which is to be metered into an exhaust gas region of an internal combustion engine.